EXERCISE 4: Endocrine System Physiology
Activity 1: Metabolism and Thyroid Hormone
Normal rat
Thyroidectomized
rat
Hypophysectomized
rat
Weight (g)
Variable, 249–251
Variable, 244–246
Variable, 244–246
ml O2 used in 1
minute
Variable, 7.0–7.2
Variable, 6.2–6.4
Variable, 6.2–6.4
ml O2 used per
hour
420–432*
372–384*
372–384*
Metabolic rate
1673–1735 ml
O2/kg/hr*
1512–1574 ml
O2/kg/hr*
1512–1574 ml
O2/kg/hr*
Palpation results
No mass
No mass
No mass
Weight (g)
Same as baseline
Same as baseline
Same as baseline
ml O2 used in 1
minute
Variable, 8.3–8.5
Variable, 7.7–7.9
Variable, 7.7–7.9
ml O2 used per
hour
498–510 ml
462–474 ml
462–474 ml
Metabolic rate
1984–2048 ml
O2/kg/hr
1878–1943 ml
O2/kg/hr
1878–1943 ml
O2/kg/hr
Palpation results
No mass
No mass
No mass
Weight (g)
Same as baseline
Same as baseline
Same as baseline
ml O2 used in 1
minute
Variable, 7.9–8.1
Variable, 6.2–6.4
Variable, 7.7–7.9
ml O2 used per
hour
474–486 ml ml
O2/kg/hr
372–384 ml
462–474 ml
Metabolic rate
1904 ml O2/kg/hr
1512–1574 ml
O2/kg/hr
1878–1943 ml
O2/kg/hr
Palpation results
1904 ml O2/kg/hr
Mass
No mass
Mass
Baseline
With thyroxine
With TSH
With
propylthiouracil
Weight (g)
Same as baseline
Same as baseline
Same as baseline
ml O2 used in 1
minute
Variable, 6.2–6.4
Variable, 6.2–6.4
Variable, 6.2–6.4
ml O2 used per
hour
372–384 ml
372–384 ml
372–384 ml
Metabolic rate
1482–1542 ml
O2/kg/hr
1512–1574 ml
O2/kg/hr
1512–1574 ml
O2/kg/hr
Palpation results
Mass
No mass
No mass
* Data populated
by student
calculations.
Part 1
1. Which rat had the fastest basal metabolic rate (BMR)? The normal rat had the fastest basal metabolic rate
because it was not missing its pituitary gland or its thyroid gland.
2. Why did the metabolic rates differ between the normal rat and the surgically altered rats? How well did the
results compare with your prediction? The normal rat has the highest BMR because it has the glands
required to stimulate and regulate the release of thyroid hormones.
3. If an animal has been thyroidectomized, what hormone(s) would be missing in its blood? For the
thyroidectomized rats the hormones missing will be triiodothyronine and thyroxine.
4. If an animal has been hypophysectomized, what effect would you expect to see in the hormone levels in its
body? For the hypophysectomized rat, the TSH will be missing due to the missing pituitary gland.
Part 2
5. What was the effect of thyroxine injections on the normal rat’s BMR? The levels were a little off. The
normal rat was hyperthyroidic because the thyroxine increases the metabolic rate but it did not develop
goiter.
6. What was the effect of thyroxine injections on the thyroidectomized rat’s BMR? How does the BMR in this
case compare with the normal rat’s BMR? Was the dose of thyroxine in the syringe too large, too small, or
just right? The BMR increased for the thyroidectomized rat with thyroxine injections. The BMR was still a
little bit below the normal rat’s BMR with thyroxine. The dose was too low.
7. What was the effect of thyroxine injections on the hypophysectomized rat’s BMR? How does the BMR in
this case compare with the normal rat’s BMR? Was the dose of thyroxine in the syringe too large, too small,
or just right? The BMR increased for the hypophysectomized rat with thyroxine injections. The BMR was
still a little bit below the normal rat’s BMR with thyroxine. The dose was too low.
Part 3
8. What was the effect of thyroid-stimulating hormone (TSH) injections on the normal rat’s BMR? The effect
of TSH was to increase the normal rat’s BMR.
9. What was the effect of TSH injections on the thyroidectomized rat’s BMR? How does the BMR in this case
compare with the normal rat’s BMR? Why was this effect observed? There was no effect on the
thyroidectomized rat’s BMR with the injection of TSH because there was no thyroid gland to stimulate.
10. What was the effect of TSH injections on the hypophysectomized rat’s BMR? How does the BMR in this
case compare with the normal rat’s BMR? Was the dose of TSH in the syringe too large, too small, or just
right? The hypophysectomized rat BMR increased with TSH. The BMR was just below the normal rat but
still lower. the syringe amount was a little too low.
Part 4
11. What was the effect of propylthiouracil (PTU) injections on the normal rat’s BMR? Why did this rat
develop a palpable goiter? The effect of PTU injections on the normal rat was to decrease the BMR. The
palpable goiter was due to the buildup of the precursors to thyroxine.
12. What was the effect of PTU injections on the thyroidectomized rat’s BMR? How does the BMR in this case
compare with the normal rat’s BMR? Why was this effect observed? The effect of PTU injections on the
thyroidectomized rat was not visible because there was no thyroid gland to be affected.
13. What was the effect of PTU injections on the hypophysectomized rat’s BMR? How does the BMR in this
case compare with the normal rat’s BMR? Why was this effect observed? The effect of PTU injections on
the hypophysectomized rat was not visible because the rat is missing the pituitary gland.
Activity 2: Plasma Glucose, Insulin, and Diabetes Mellitus (pp. 64–67)
Chart 2.1 Glucose Standard Curve Results
Tube
Optical density
Glucose (mg/dl)
1
0.30
30
2
0.50
60
3
0.60
90
4
0.80
120
5
1.00
150
Chart 2.2 Fasting Plasma Glucose Results
Sample
Optical density
Glucose (mg/dl)
1
0.73
104
2
0.79
115
3
0.89
131
4
0.83
122
5
0.96
143
1.What is a glucose standard curve, and why did you need to obtain one for this experiment? Did you correctly
predict how you would measure the amount of plasma glucose in a patient sample using the glucose
standard curve? The glucose standard curve correlates the intensity of the color obtained and measured on
a spectrophotometer (optical density) to the glucose concentration.
2. Which patient(s) had glucose reading(s) in the diabetic range? Can you say with certainty whether each of
these patients has type 1 or type 2 diabetes? Why or why not? Patients 3 and 5 had a fasting plasma glucose
in the diabetic range. It is not possible to tell if they have type 1 or type 2 just from their fasting plasma
glucose.
3. Describe the diagnosis for patient 3, who was also pregnant at the time of this assay. This would be
described as gestational diabetes. The diabetes often disappears after the pregnancy.
4. Which patient(s) had normal glucose reading(s)? Patients 1 and 2 were in the normal range.
5. What are some lifestyle choices these patients with normal plasma glucose readings might recommend to
the borderline impaired patients? Limit the ingestion of simple sugars. Choose “good” carbohydrates such
as whole wheat and fiber based carbohydrate choices.
Activity 3: Hormone Replacement Therapy
Rat
T score
Contro
Variable, –2.81 to –2.85
Estrogen
Variable, –1.52 to –1.74
Calcitonin
Variable, –2.05 to –2.35
1. Why were ovariectomized rats used in this experiment? How does the fact that the rats are ovariectomized
explain their baseline T scores? The ovaries produce estrogen and estrogen stimulates bone growth. Without
estrogen bone growth is impaired and osteoporosis is a common result.
2. What effect did the administration of saline injections have on the control rat? How well did the results
compare with your prediction? The saline had no effect. The inclusion of the saline as a negative control is
to insure that saline has no effect.
3. What effect did the administration of estrogen injections have on the estrogen-treated rat? How well did the
results compare with your prediction? The estrogen injections did increase the rat’s vertebral bone density
as predicted and as indicated by the negative T score.
4. What effect did the administration of calcitonin injections have on the calcitonin-treated rat? How well did
the results compare with your prediction? The calcitonin showed no change in the vertebral bone density.
This is somewhat contradictory to what is expected. We do not know why.
5. What are some health risks that postmenopausal women must consider when contemplating estrogen
hormone replacement therapy? Health risks of estrogen therapy include an increased incidence of uterine
cancer, breast cancer and blood clots.
Activity 4: Measuring Cortisol and Adrenocorticotropic Hormone
Patient
Cortisol
(mcg/dl)
Cortisol level
ACTH (pg/ml)
ACTH level
1
Variable, 3±1
Low*
Variable, 18±2
Low*
2
Variable, 35±5
High*
Variable, 13±2
Low*
3
Variable, 45±5
High*
Variable, 86±5
High*
4
Variable, 3±1
Low*
Variable, 100±5
High*
5
Variable, 50±5
High*
Variable, 18±2
Low*
* The entries in these columns are designated by the student in the software.
1. Which patient would most likely be diagnosed with Cushing’s disease? Why? Patient 3 would be diagnosed
with Cushing’s disease because the levels of cortisol and ACTH are both high.
2. Which two patients have hormone levels characteristic of Cushing’s syndrome? Patients 2 and 5 both have
high levels of cortisol and low ACTH. These levels are characteristic of Cushing’s syndrome.
3. Patient 2 is being treated for rheumatoid arthritis with prednisone. How does this information change the
diagnosis? The diagnosis would change to iatrogenic or physician-induced Cushing’s syndrome.
4. Which patient would most likely be diagnosed with Addison’s disease? Why? Patient 4 would be diagnosed
with Addison’s disease because the level of ACTH is high but the level of cortisol is low.